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How to Integrate PayPal Website Payments Standard with ASP.Net

Yesterday was the South Florida Code Camp 2010 in Miramar (that’s between Miami and Ft. Lauderdale). I gave a presentation on integrating PayPal Website Payments Standard with ASP.Net C#. I included a demo web application showing four different options to program the application though from the buyer’s point of view, all four examples looked and acted the same.CodeCampImage1


PayPal standard is the familiar option that displays PayPal buy-buttons to the buyer and when clicked, control is transferred to PayPal for the buyer to complete the payment and hopefully return to the website.

Each Buy Now button is a <form> with some hidden <input> fields and the button <img>. The four examples show different ways to implement or create the <form> fields. The first two examples redirect directly to PayPal as specified by the form’s action parameter and the last two examples post to an aspx page that controls building the post form to cause the redirect to PayPal.

  • Example 1 – This page builds the form and fields and may be seen with a View Source. This is easy and can be dynamically built by the code but may be hacked by a user that can copy and modify the page source (like the amount field) to buy your product or service at whatever price they want. Automated fulfillment sites may miss this fraudulent purchase.
  • Example 2 – The seller used PayPal’s button factory to build a hosted button. This solves the security issue but at the expense of the dynamic nature of the form field generation and the issue of manually having to create a button for every product of your inventory. View Source shows the main field in the form is the identifier of the hosted button.
  • Example 3 – In this example, clicking the button does not sent the buyer to PayPal immediately (though it appears that way to the buyer). View source will only show the product’s ID is passed in the form which calls PayPalRedirector.aspx. The aspx page looks up the product in the database to get its name, price, etc. and builds the html needed by PayPal (much the same as seen in Example 1. It pushes this html to the buyer’s browser with an automatic form submit. This is a bit more secure than Example 1 but a knowledgeable user can capture the generated html to forge a similar fraudulent order.
  • Example 4 – This final example solve the hackability problem and still allows dynamic buttons to be generated. The button form is generated as in Example 3 but is encrypted before sending the redirect form to the buyer’s browser. This does require that the seller obtain an encryption certificate and upload the public key to PayPal so PayPal can decrypt your button.

The PayPalRedirector.aspx code used in Examples 3 and 4 used a class library (PayPalStdLib) I wrote to allow easy strongly-typed access to build and initialize the object with the payment parameters and a method to initiate the redirect to PayPal. This is a bare-bones class you can enhance with additional properties as needed for your own use.

The presentation was the last of the day but was well attended by a lively group who had many questions. See my article about PayPal Encrypted Website Payments for additional information about that part of the code in Example 4. Source code and PowerPoint slides are available at

Plug: Webguild does PayPal development, integration and consultation including full-blown PayPalStdLib and PayPalProLib class libraries.

Print | posted on Sunday, February 28, 2010 12:00 AM | Filed Under [ Programming ]



# re: How to Integrate PayPal Website Payments Standard with ASP.Net

Thank you so much,
plz give me step by step process PAYPAL integration in,
I am new this one
plz help me step by step process

Thank you,
8/17/2012 2:54 AM | ANIL

# re: How to Integrate PayPal Website Payments Standard with ASP.Net

This is awesome!! Really helpful for me and developers. Thanks for sharing with us. Following links also helped me to complete my task.
6/13/2013 8:20 AM | Batra Somesh

# re: How to Integrate PayPal Website Payments Standard with ASP.Net

Really love it
7/31/2013 3:29 PM | heinrich

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